Spinal muscular atrophy (SMA) is a motor neuron disease for which no effective treatment is currently available. SMA is caused by reduced levels of the evolutionarily conserved and ubiquitously expressed survival of motor neuron (SMN) protein. SMN together with several other core proteins forms the macromolecular SMN complex, which functions in the assembly of ribonucleoproteins (RNPs). While SMN is believed to assemble a variety of RNPs, to date its only well-characterized function is in the assembly of spliceosomal small nuclear ribonucleoproteins (snRNPs), critical components of the eukaryotic mRNA splicing machinery. Disruption of an SMN-dependent RNA splicing pathway has not yet been able to explain the underlying disease mechanisms in SMA, highlighting the significance of identifying additional pathways controlled by SMN. Our preliminary work identifies the assembly of the U7 snRNP - a RNP factor required for 3'-end processing of replication dependent histone mRNAs - as SMN-dependent in vivo. Disruption of this pathway due to SMN deficiency causes deregulation of histone synthesis with potentially detrimental effects on downstream cellular processes. This research project aims to build on these findings to identify the critical RNA and protein determinants of SMN-mediated U7 snRNP biogenesis, as well as to determine whether altered histone synthesis caused by U7 dysfunction contributes to cellular phenotypes caused by SMN deficiency, including motor neuron survival. Taken together, this project aims to characterize an SMN-dependent RNA pathway that is disrupted is SMA and may have deleterious cellular consequences with important implications in etiology of the disease. ! ! PUBLIC HEALTH RELEVANCE: Spinal muscular atrophy (SMA), a childhood neurodegenerative disease for which no effective treatment is currently available, is caused by a deficiency in the survival motor neuron (SMN) protein. To identify targets for effective SMA therapeutics, it is essential to characterize the fundamental biological pathways controlled by SMN. This project aims to characterize a novel SMN-dependent pathway that is disrupted in the disease in an effort to reveal novel disease mechanisms, which may provide new avenues for SMA therapeutic targeting.